Biological Mechanisms of Tooth Movement. Группа авторов
of the duration and outcome of orthodontic treatment. The ever‐growing flow of basic information into the orthodontic domain promotes the adoption of the concept of “personalized medicine” (Kornman and Duff, 2012). The main investigative tool in this regard is molecular genetics, which has been used successfully in oncology in the search for faulty genes, responsible for the initiation, growth, and dissemination of a variety of tumors. This approach is growing in significance in medicine and is beginning to occur in dentistry. Orthodontics, where genetics plays a major role in determining the morphology and physiology of the orofacial region, is a natural candidate to use this rapidly expanding body of basic information in order to formulate treatment plans that fit closely the biological features of each individual patient.
Conclusions and the road ahead
Orthodontics started with the use of a finger or a piece of wood to apply pressure to crowns of malposed teeth. The success of those manipulations proved convincingly that mechanical force is an effective means to correct malocclusions. Until the early years of the twentieth century, understanding the reasons why teeth move when subjected to mechanical forces was only a guess, based on reason and empirical clinical observations. Farrar hypothesized in 1888 that teeth are moved orthodontically due to resorption of the dental alveolar socket and/or bending of the alveolar bone. Both hypotheses were proven to be correct during the twentieth century, as orthodontic research has spread into increasingly fundamental levels of biological basic research. The rationale for these basic investigations was the wish to unveil the mechanism of translation of mechanical signals into biological/clinical responses; the etiology of iatrogenic effects resulting from OTM; and to discover efficient means to shorten significantly the duration of OTM. Many details on the behavior of cells involved in OTM have emerged from those investigations but, despite this progress, the final answer to the above issues remains elusive.
At present, molecular biology and molecular genetics remain at the cutting edge of orthodontic research. Multiple genes that may be involved in the cellular response to mechanical loads have been identified (Reyna et al., 2006), and genes associated with orthodontic‐induced root resorption (Abass and Hartsfield, 2006). The role played by specific genes in OTM was revealed by Kanzaki et al. (2004), who reported that a transfer of an OPG gene into the PDL in rats inhibits OTM by inhibiting RANKL‐mediated osteoclastogenesis. According to Franceschi (2005), future efforts in dental research will include genetic engineering, focusing on bone regeneration. Recently, Zhao et al. (2012), through experiments in male Wistar rats, reported inhibition of relapse with local OPG gene transfer through the inhibition of osteoclastogenesis.
The body of knowledge that has evolved from multilevel orthodontic research supports the notion that the patient’s biology is an integral part of orthodontic diagnosis, treatment planning, and treatment. Therefore, orthodontic appliances and procedures should be designed to address the patient’s malocclusion in light of his/her biological profile, in much the same fashion as is done by medical specialists in other fields of medicine. As outlined by Jheon et al. (2017), analyses of genetic and molecular factors may soon uncover indicators predicting slow tooth movement, increased predisposition to root resorption, and accelerated late stage skeletal growth. Patients will be provided with customized appliances printed through the treatment stages, as per the devised virtual plan. In addition, specific biologic/pharmacologic agents based on patients’ molecular and genetic background will be delivered to enhance treatment efficiency and outcomes.
Orthodontics started in ancient times by pushing malposed teeth with a finger for a few minutes a day, but today we know that the reason teeth can be moved is because cells respond to changes in their physical and chemical environment. Research will continue to unravel new details of this process, and the beneficiaries will be all people seeking and receiving orthodontic care.
References
1 Abass, S. K. and Hartsfield, J. K. Jr. (2006) Genetic studies in root resorption and orthodontia, in Biological Mechanisms of Tooth Eruption, Resorption, and Movement (eds Z. Davidovitch, J. Mah, and S. Suthanarak). Harvard Society for the Advancement of Orthodontics, Boston, pp. 39–46.
2 Asbell, M. B. (1990) A brief history of orthodontics. American Journal of Orthodontics and Dentofacial Orthopedics 98(2), 176–183.
3 Asbell M. B. (1998) John Nutting Farrar 1839–1913. American Journal of Orthodontics and Dentofacial Orthopedics 114, 602.
4 Bartzela, T., Turp, J. C., Motschall, E. and Maltha, J. C. (2010) Medication effects on the rate of orthodontic tooth movement: A systematic literature review. American Journal of Orthodontics and Orofacial Orthopedics 135, 16–26.
5 Bassett, C. A. L. and Becker, R. O. (1962) Generation of electrical potentials in bone in response to mechanical stress. Science 137, 1063–1064.
6 Baumrind, S. (1969) A reconsideration of the propriety of the “pressure‐tension” hypothesis. American Journal of Orthodontics 55, 12–22.
7 Bien, S. M. (1966) Hydrodynamic damping of tooth movement. Journal of Dental Research 45, 907–914.
8 Bister, D. and Meikle, M. C. (2013) Re‐examination of “Einige Beiträge zur Theorie der Zahnregulierung” (Some contributions to the theory of the regulation of teeth) published in 1904–1905 by Carl Sandstedt. European Journal of Orthodontics 35, 160–168.
9 Caster, F. M. (1934) A historical sketch of orthodontia. Dental Cosmos 76(1), 110–135.
10 Davidovitch, Z., Finkelson, M. D., Steigman, S. et al. (1980c) Electric currents, bone remodeling, and orthodontic tooth movement. II. Increase in rate of tooth movement and periodontal cyclic nucleotide levels by combined force and electric current. American Journal of Orthodontics 77, 33–47.
11 Davidovitch, Z., Gogen, M. H., Okamoto, Y. and Shanfeld, J. L. (1992) Neurotransmitters and cytokines as regulators of bone remodeling, in Bone Biodynamics in Orthodontic and Orthopedic Treatment (eds D. S. Carlson and S. A. Goldstein). University of Michigan Press, Ann Arbor, MI, pp. 141–162.
12 Davidovitch, Z., Korostoff, E., Finkelson, M. D. et al. (1980a) Effect of electric currents on gingival cyclic nucleotides in vivo. Journal of Periodontal Research 15, 353–362.
13 Davidovitch, Z., Montgomery, P. C., Eckerdal, O. and Gustafson, G. T. (1976) Demonstration of cyclic AMP in bone cells by immuno‐histochemical methods. Calcified Tissue Research 19, 317–329.
14 Davidovitch, Z., Montgomery, P. C., Yost, R. W. and Shanfeld, J. L. (1978) Immunohistochemical localization of cyclic nucleotides in the periodontium: Mechanically‐stressed osteoblasts in vivo. The Anatomical Record 192, 351–361.
15 Davidovitch, Z., Okamoto, Y., Gogen, H. et al. (1996) Orthodontic forces stimulate alveolar bone marrow cells. In: Biological Mechanisms of Tooth Movement and Craniofacial Adaptation (eds Z. Davidovitch and L. A. Norton). Harvard Society for the Advancement of Orthodontics, Boston, pp. 255–270.
16 Davidovitch, Z., Steigman, S., Finkelson, M. D. et al. (1980b) Immunohistochemical evidence that electric currents increase periosteal cell cyclic nucleotide levels in feline alveolar bone in vivo. Archives of Oral Biology 25, 321–327.
17 Fauchard, P. (1728) Le chirurgien dentiste ou traite des dents (trans. Lilian Lindsay). Butterworth, London.
18 Franceschi, R. T. (2005) Biological approaches to bone regeneration by gene therapy. Journal of Dental Research 84, 1093–1103.
19 Gillooly, C. J., Hosley, R. T., Mathews, J. R. and Jewett, D. L. (1968) Electrical potentials recorded from mandibular alveolar bone as a result of forces applied to the tooth. American Journal of Orthodontics 54, 649–654.
20 Gluhak‐Heinrich, J., Ye, L., Bonewald, L. F. et al. (2003) Mechanical loading stimulates dentin matrix protein 1 (DMP1) expression in osteocytes in vivo. Journal of Bone and Mineral Research 18, 807–817.
21 Grimm, F. M. (1972) Bone bending, a feature of orthodontic tooth movement. American Journal of Orthodontics 62, 384–393.
22 Jheon, A. H., Oberoi, S., Solem, R. C. and Kapila, S. (2017). Moving towards